it's not the same volume with the speaker disconnected. it's much lower
I tried the shorting on the amp with the same results (using both the autotek, a Concept, and a sony amp)

I'm at a complete lost.

 

nice as they may be , could your custom brackets be to blame? they are aluminum, right?

just a thought.

 

They are aluminium, however I had the speakers out of the car, with the stock speakers hooked up in the back of the car (you can see them in the pic) and still got the noise...

 

So have you beaten this one yet? Any updates?

 

Nope, I've put the car back together with just the head unit directly powering the speakers. A friend of mine owns a stereo shop here, and he's offered to let me bring the car over with the stereo, amp, and speakers, and he and his techs would help me free of charge figure out what's causing it all.
I'll probably take it over next weekend. It sounds great with just the head unit right now, although I really miss my subwoofer

 

What head unit did you install? Have you got a picture with the trim kit?
Also, who made those 6 x 9 to 6-1/2" adapter plates?

 

I went with a Pioneer DEH-P8600MP. The adapters were made by a friend of mine at work (I work at an aircraft manufacturing company, so they're 'aircraft grade aluminium.. ooooo, heh)

No pictures yet, will take some today and put them up.

 

Have you had any luck with the noise yet?